The present invention relates to an electromagnetically actuated fuel atomisation and metering valve intended to be utilized on a fuel injection device of an internal combustion engine, which has very reduced dimensions, can be mounted in a simple and rapid manner, be extremely reliable and have very short response times to activation signals.
As is known valves of this type normally include a casing, a shutter member movable axially within the interior of this, from a first position in which it opens the fuel injection passage formed in the forward end of the casing itself, to a second position in which it closes this passage, a core of magnetic material disposed within the interior of the casing and an armature fixed to the shutter member, as well as an excitation winding of annular form for generating a magnetic field in the core to attract the armature and carry the shutter member into the previously defined first position.
The said core is normally fixed to the upper end of the casing utilizing connection members of various types and sealing rings are also disposed between the former and the latter for preventing the escape of fuel from the valve casing.
The shutter member is normally held in the previously defined first position by the action of a coil spring housed within an axial bore in the core and one end of which rests on a stop member fixed to the core itself; this stop member, which can be one of various types, is also normally axially adjustable in position with respect to the core for the purpose of being able to vary the force exerted by the said spring on the shutter member.
Valves of the type briefly described have various disadvantages.
First of all, the operating characteristics of the valve can vary in use because of an excessive heating of the excitation winding: in fact, it can be completely drawn into the interior of a cavity in the casing and the fuel exerts a very modest cooling action on it because of the small surface of the winding which is exposed to the washing action of the fuel itself.
Moreover, the time required for the shutter member to move from one to the other of its two previously defined positions can be rather long because of the large magnetic inertia of various parts of the valve, in particular the core; the mass of this is rather large because of the form and dimensions which are necessary for fixing it to the end of the casting and due to the presence of the auxiliary members necessary to effect connection between the parts and to ensure a fuel tight seal between the casting and the core. Consequently, therefore, the overall dimensions of the valve are rather large.
Finally, the operations necessary for assembly of the valve are neither rapid nor easy since the various members of which it is constituted must be mounted from both ends of the casing and, moreover, a rigorous regulation of the axial position of the first defined stop member must be effected during the course of the assembly. In order to achieve this regulation it is necessary that the stop member and the other subsidiary members which are necessary to define the said axial position be accessible from the upper end of the valve, with consequent restrictions on the form and dimensions of this upper part.